Mercury is the closest planet to the Sun in the Solar System and is also the smallest planet. Since it is the closest planet to the Sun, its orbit is the smallest and so Mercury takes 88 Earth days to revolve around the Sun. It is also the hottest planet because of its proximity to the Sun. It has no atmosphere and there is no trace of water, so life is not possible on this planet. Since it is within the Earth's orbit, it is visible in the morning and evening sky as a bright object. Being a non-luminous body, it reflects light from the Sun.